NEONATAL IRRADIATION AND LEARNING 663 



survivors. As some irradiated animals died, the behavioral testing was com- 

 pleted on the selected population which survived. 



Mortality was directly proportional to amount of radiation, for both the 

 AET and unprotected groups. The protective effect of AET was most notice- 

 able in the 275 r group, where 118 unprotected rats were radiated to obtain 

 35 rats surviving 45 days, whereas only 66 chemoprotected animals were 

 required to yield 30 survivors (or 30% and 46%, respectively) . 



The mean survival rate appeared greatest for animals radiated at 4 and 

 6 days, and it is in these groups that the protective effect of AET was most 

 clearly demonstrated. Mortality was highest in the 2 day group, and for this 

 group no protective effect was observed. 



Weight 



Separate comparisons of group mean weights were made for males and 

 females. The nonirradiated group averaged 135.4 gm (males) and 106.5 gm 

 (females). The irradiated group averaged 97.5 gm (males) and 82.6 gm 

 (females). A comparison of the unprotected (saline) groups for the three 

 radiation levels indicated that weight decrements in both sexes increased as 

 radiation dose was increased. The protective effect of AET on weight gain 

 was most noticeable at the 275 r level. 



Considering age at radiation, the greatest weight decrements appeared 

 in the 2 and 6 day groups. 



Original Learning 



Three performance measures — trials, errors, and time in the maze — were 

 used for analysis of the original learning scores in the Lashley III maze. The 

 function relating dose level to performance (Fig. 1) indicated that perform- 

 ance deficits on all measures increased with increasing radiation dose. 



Substantial decrements in maze performance appeared at the highest 

 radiation level. The performance of 275 r rats differed significantly from 

 that of nonirradiated animals {p < .01 for errors and time and < .05 for 

 trials). A similar comparison for the 225 r and nonirradiated groups re- 

 vealed no significant differences and indicated that the effects of 225 r on 

 performance were near threshold and were not very different from the r 

 group. 



A trend is visible in the curves of Fig. 1, and the ordering appears con- 

 sistent in all cases. Superimposed in the graph of trials are data taken from 

 the previous neonatal study (Levinson and Zeigler, 1959) ; there is consid- 

 erable agreement between the results of the two studies. 



As in the previous study, time and error scores were more sensitive indi- 

 cants of radiation effects than trials. 



